Bar codes have become a common means for identification of articles, conveying serial numbers, and other relatively short items of data. There are a number of different bar codes in common use, such as; the UPC code found on most packages in grocery stores; the 2 of 5 code, Codabar, Code 39 widely used for non grocery product identification and other applications; Code 93, similar to Code 39 but with the capability of encoding the full ASCII character set. These codes all carry their information in the linear domain along the code pattern. Various means are used to define the ones and zeroes of the binary code patterns. In some cases a narrow bar or space is a zero bit, while a wide bar or space is a one bit. Other combinations of bars and spaces are also used.
Another bar code is also in common usage by the US Postal System. This bar code carries its information in the height of each bar of the bar code, with all marks and spaces of equal width and used only for timing purposes. In this system a short bar is a zero and a tall bar is a one. This is the only commonly used code with vertical modulation.
This invention recognizes that these two methods of coding are orthogonal and that therefore a coding system can be devised which combines these coding approaches to provide either more code characters in the same physical space, or permit the conveyance of the same information in two different methods for greater reliability in code printing/reading. This invention provides a method for incorporating the two code streams into one pattern, and a method for separating these code streams during the reading process.